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FleaPlus writes "The German Aerospace Center is planning to launch a novel reusable spacecraft in 2011, incorporating flat, damage-resistant tiles. Nitrogen will be pumped through the porous tiles, creating a protective gas layer that actively cools and shields the hottest parts of the spacecraft from the searing heat of reentry. The €12.5M unmanned 'SHEFEX II' project is a major technological step toward the team's eventual goal of a reusable space glider, which will be cheaper and easier to build than NASA's space shuttle."

That's not entirely true; it's more of a US excuse during the space race. The US was very successful with Operation Paperclip [wikipedia.org], which was an attempt to make sure that the US, not the USSR, got most of the German rocket scientists (as well as several whole V2 rockets). The Soviets got a few German rocket scientists (most notably, Helmut Gröttrup, Wernher von Braun's assistant), but not many. Most of the people they got were low level people, mainly on the assembly lines. They were primarily interrogated for information and little used beyond that point. After 1951, not even Gröttrup was allowed to assist in their rocket program any more, and he was returned to Germany in 1953 -- back when von Braun was just starting to become a big rocketry name in the US, and well before his tenure as NASA's first director (1960-1970).

There's a nice bon mot about this: "The Soviets got the Germans who knew how it worked, the US the Germans who knew why it worked."

This sums it up surprisingly well, and also explains (while of course ignoring lots of other relevant stuff) why the Soviets
made it up there quite fast, but after this failed to make significant progress for quite a while.

Not at all. All but the first couple post-WWII Soviet rockets were *very* different from the V2. The R1 was basically a V2 replica, but the R7 was based on Korolyov's pre-war designs.

We always seem to be looking for ways to downplay the Soviet achievements in space in the 1950s and early 1960s. Why is that? Is it too much to accept that there were some *really damned good Soviet rocket scientists* over there? Had they not been majorly underfunded compared to the US in the moon race, and had they not made a couple of key design blunders with the N1, they likely would have beaten us in that, too. The loss of Korolyov in the middle of the project didn't help, either.

The reality is that it was the *US* that was heavily reliant on German rocket scientists and German technology, to a much greater extent than the Soviets. We shipped over three hundred freaking train loads of V2 parts back to bootstrap our space program. We took almost all of their top scientists (most Germans were scared of the Soviets, and the US offered big incentives).

Really, had the N1 development process been fully prioritized and properly funded, it could have been an excellent craft. The lack of testing made it poorly handle failures which, when you have that many engines, is almost inevitable. Each time, a single problem took down the whole craft. But the craft was very innovative -- staged combustion engines arranged in a way that formed a primitive aerospike airbreather, for example. Pre-heated fuel from the regenerative cooling was preburned to run the pumps

The Saturn was Von Braun's design. The LVDC program that guided the Saturn was a port of a FORTRAN program that implemented a set of control laws and arithmetic written by the Germans. The rest of the program was mostly US design. The Germans had relatively little to do with the CSM and LM. Their job was to get things into space and to a lesser extent down again, but dealing with it once it was in space was beyond their original research. We paid for the entire

There is no need for glider-based spacecraft. Wings are useless in space. "man-rated" launch vehicles cost something like $10k per pound to go to orbit. The extra pounds for wings are a massive waste of money and resources.

The original design--The Capsule--was the right idea! Why not build a re-usable capsule?

Capsules are great if you don't mind landing in an ocean or a desert; someplace big and empty.

However, if you would like the efficiencies created by being able to land your spacecraft someplace specific and useful near a population center, like a spaceport or airport, than wings are just the ticket.

What are you babbling about? 1. gives quite nice determination of geographic area (it's good enough for Soyuz capsules to be often recorded on video while descending on parachutes by retrieval crews, so quite exact) 2. Have you read even a snipped of those links? Those were tests of a recovery system for a manned spacecraft.

(Maybe we could even make a religious tweak, such as:1) Sign up and end your life as an astronaut, become a hero!)2) Shoot people up in space when we need something fixed.3) Let them fix it.4) Leave them.5) Profit!

Indeed -- look at the history of capsules -- the sinking of Mercury 4, the Voskhod 2 crew's night surrounded by wolves, Soyuz 18a's high-G roll that nearly sent it tumbling off a 500' cliff, etc.

I think the best example is Soyuz 23: a mistargetted landing led to the capsule landing on a frozen lake and crashing through the ice. No problem as it was designed to float, right? Well, the parachute got wet and, weighed down, dragged the capsule upside down. The vent tube -- open, as per standard practice -- now began to fill the craft with ice-cold water. The cosmonauts luckily stopped it up before it sent the craft to the bottom. So there they waited, half submerged, upside down in a frozen lake, with no air, in -22C weather. They had to cut way their space suits and get into clothes so as not to freeze; it took an hour and a half. They relied on regenerated air, and did everything possible to conserve power -- they'd leave the system off until they nearly blacked out from the CO2, then turned it on just long enough to clear up. Nonetheless, they still ran out of power. Helicopters couldn't land in the blowing mist, and rescue attempts failed until they ultimately got a hook on the parachute and dragged the craft half a dozen kilometers across the frozen landscape before they could be rescued.

Now, consider what happens to a spaceplane in such scenarios - a need to ditch (this was considered a loss of crew for the Shuttle); "landing" in wilderness; or relying on succesfull automatic recovery in the case of launcher failure during ascent (hm, where did I hear about such scenario in a spaceplane...) & with recovery systems working perfectly, despite discrepancy between assumed and encountered acceleration on the order which torns apart winged vehicles. Also, take note of how good winged vehicle

Well, with "spaceplane" your're adding the amount of things to go wrong.

For example, asphyxiation that you mention is surely a hazard with all approaches (well, not really anymore, when everybody uses pressure suits). But failure of systems actively controlling descent (which does happen on Soyuz from time to time) - and the results are quite dramatically different.

However, if you would like the efficiencies created by being able to land your spacecraft someplace specific and useful near a population center, like a spaceport or airport, than wings are just the ticket.

Not just that. Capsules don't scale well. Building a heat shield that burns up on reentry is fine if you're flying once in a while with three or four people. It doesn't work well for a space plane to carry a hundred people on a daily basis. In the long run, we need something that's truly reusable.

Did you miss how this story is about non-ablative ("non-burning") heatshield? Also, while capsules might have some not too big size limit (we're probably nowhere near yet), there's also another approach without wings - lifting bodies; which aren't that dissimilar to a capsule flying lifting reentry, just a bit more optimised one... But no wings.

IIRC, what matters most as far as how much heat per square inch during reentry is the mass to surface area ratio. A wing-based design allows you to have minimal support structure for a large portion of the vehicle, which allows you to add a lot of surface area without adding a lot of mass.

Even with a non-ablative heat shield, a capsule design still gets insanely hot on the outside. I'm pretty sure you'd end up having to change the tiles out fairly frequently or the material is going to fracture from the d

The original design--The Capsule--was the right idea! Why not build a re-usable capsule?

You're assuming that all spacecraft have the same mission requirements. The Space Shuttle was originally intended, IIRC, to be able to take things to orbit, and OPTIONALLY RETURN THINGS FROM ORBIT. A space capsule will only be able to return humans and -very small items-. No going to orbit, picking up a broken or obsolete satellite or space telescope, bringing it back for fixes or refurbishment, and returning it to orbit on another flight. If all you're doing is sending stuff up, and then returning only people, then yeah, a capsule can do that job; but that's not the only job that needs doing.

NASA as a publicity fund raising stunt should save one shuttle's worth of parts and go retrieve the Hubbell Space telescope instead of crashing it into the ocean. Have the shuttle land and the load it directly for a flight to DC. Giving the whole pile (shuttle with Hubbell inside) to the Smithsonian.

Now that would be an awesome display. Heck I would donate money to help make that happen. To bad NASA doesn't think like awesome anymore.

Hubble can not be returned with any of the remaining space shuttles - they all have an airlock to dock to ISS permanently mounted in the payload bay. The last shuttle that would have had enough room to transport Hubble would have been Columbia.

There is currently no need for MANNED spacecraft, because supporting humans limits their ability to do "everything else" including actual exploration.The glacial development cycles mandated by the need to return meat tourists cost so dearly that useful "remote manned" missions won't be funded.

Because the USAF wanted the Shuttle to be able to use the atmosphere to break and turn back. This way, when launched in a polar orbit, it would be able to turn back and capture GLONASS or Russian Spy Satellites without appearing on the russian radar. Of course, the final design wasn't able to do such a manouver so the USAF has no use for it. But the design stick.

Considering orbits of GLONASS satellites (and probably many spy ones), simple orbital mechanics make performing such mission in a covert manner an impossibility; nvm the inability of the design to break LEO.

Plus so simple and effective countermeasures, from so cheap and numerous (comparatively) "targets" - maybe millitary intelligence works after all, sometimes;) (not quickly enough to not give us Shuttle though)

+4 Interesting? This not only isn't interesting - it's utter and complete innumerate and ill educated hogwash.The Shuttle cannot 'turn back' once it reaches orbit (thus avoiding Russian radars). It can 'turn back' in the atmosphere (shortly after launch), but in that event it gets nowhere near orbit and thus cannot snag a satellite.

What the USAF wanted the Shuttle to do was do a 'one orbit' launch out of Vandenburg, inspect or grab a Soviet satellite, and then landing again in US territory

Actually, if you take a look at their basic development strategy [www.dlr.de] (near the bottom of the page), it looks like there's a few different directions they're interested in potentially taking this: a suborbital microgravity platform, a suborbital point-to-point transportation, and orbital transportation. In the case of microgravity research you want to be able to launch often, so returning to a landing strip makes that easier and more economical. Same for point-to-point transportation: if you're delivering cargo

There is no need for glider-based spacecraft. Wings are useless in space. "man-rated" launch vehicles cost something like $10k per pound to go to orbit. The extra pounds for wings are a massive waste of money and resources.

I suspect this has to do with the idea that anything except Single Stage To Orbit [wikipedia.org] And Back is not a "real" spacecraft. And that requires controlled landing, which requires either power to slow descend or wings to glid with.

Atmospheric nitrogen [wikipedia.org], on the other hand is remarkably stable. At very high temperatures, (such as you might find at the leading edges of a reentry vehicle) nitrogen can be oxidized to to various forms of NOx. These can form acids in solution, but not in concentrations high enough to worry about.

And when you consider that there is plenty of naturally-available nitrogen in the atmosphere, this small addition probably isn't enough to worry about.

You're probably talking about the transpiration cooling that Gary proposed for his Phoenix series of SSTOs. That would have worked even better than nitrogen gas cooling, given the extra heat soaked up by the water flashing to vapor. The transpiration cooling struck me as tricky because of the complex fabrication required (although much more do-able these days than in the '80s) and the need for high-purity coolant so that you don't get residue plugging the transpiration orifices (which were pretty small).

Yeah, and if there's even a slight problem with the coolant system -- the liquid turns to gas, expands 1,500x its original size... and is surrounded by ceramic, metal, plasma, and several thousand degree temperatures at a critical point on the airframe.

Yeah, and if there's even a slight problem with the coolant system -- the liquid turns to gas, expands 1,500x its original size... and is surrounded by ceramic, metal, plasma, and several thousand degree temperatures at a critical point on the airframe.

It's pretty normal for rocket engines to be regeneratively cooled with explosive fuel. This kind of approach has its flaws, but you haven't identified one of them. For a space ship during reentry every point on the airframe is critical.

However this is not a liquid cooling system of the tiles. The (liquid) gas is pumped through the tiles to the leading edge where it is expected to evaporate. So worst case should be no cooling from the gas or the gas layer as a protective layer between the tiles and the incoming atmosphere.

If designed properly if everything works it is re-useable, and if there is a failure you would hope a production model would be designed to that the tiles would survive a single use even without any gas flow.

If such cooling systems were prone to failure, we would have airliners regularly falling out of the sky. Jet engines use this same exact technique to protect their combustors and turbines. Were the film to fail, you would have maybe 30 seconds before that whole section of the engine completely melted away.

Yeah, it sounds like a useful technology, very interesting... until one of the numerous components in the system fails. Too many potential failure points for such a critical system. Will the tiles be effective if the gas system goes non-op?

I was talking to one of the engineers that developed this system to replace the leading edges of the shuttle. It is similar to what the Germans are doing but it uses heat pipes to carry the heat from the most intense heating areas to relatively cooler ares. It worked like a champ but one of the problems with the Space Shuttle Program is that is was treated like it only had 5 years left for the last 20 years. If instead we kept upgrading them and fixing the high cost items we might have something that is a l

In general, air consists of molecular Nitrogen (N2) with a volume count of 78%. To extract it you just need to cool the air until the Nitrogen liquefies. This process was discovered in the 19th century and is the base of inorganic chemistry.

I would think that the big concern with a system like this is the added weight. Is it more cost-effective to have an active cooling system such as this, but carry along the plumbing, tanks, etc.? Or is it better to simply have replaceable tiles like the shuttle, and save the weight...then have to perform all of the required maintenance to the leading edges before the next flight?

The problem with the shuttle program was really all the things that had to be done between flights. It was originally supposed to have a two week turnaround, something that turned out to be a pipe dream because of all the things that needed to be inspected and refurbished. If the Germans can make a ship that needs less inspection and maintenance, they can fly it more often. That will bring down the $/kg-to-orbit cost, which I think ought to be the goal of any serious space program at this point.

I've thought of active cooling myself.
I always wondered, if you used an active cooling system, where would
you radiate the heat? In other words, you can carry heat away from
the underside of the ship by pumping a fluid through the tiles or whatever,
but then you still have to re-radiate that heat someplace. OK, you might
be able to transform some of the heat into useful work too; but we're
talking about a lot of heat, and even if you got right to the Carnot
efficiency the waste still has to go someplace.

I never got as far as doing the "back of the envelope" calculations
on some substance with a heat capacity to absorb re-entry heat (and light
enough to carry onboard) or the more tricky calculation of how you would conduct
the heat from the underside and radiate it topside. I kind of assumed that
actual aerospace engineers had done the calcs, and decided it just wouldn't work.

Weight kills in space, so I'd be curious to know how much the system weighs
vs tiles or Russian-style ablative coatings. I'm assuming the Russians still
use ablatives. I'm sure somebody will correct me if I'm wrong.

The way I read TFA is that the N2 coolant is consumable. Rather than circulating it to a heatsink, they just expel it through pores in the surface, allowing the gas to buffer the compressed air during reentry. It brings cooling back into a convective mode.

Sure you have to refill the tanks prior to the next launch, but liquid nitrogen is (relatively) cheap.

You also have to carry all that nitrogen from the moment of launch all the way through reentry. Scrapping the wings and making a powered landing might have all the advantages of this scheme without having the complication of the nitrogen "pores".

You also have to carry all that nitrogen from the moment of launch all the way through reentry.

This is the *weight* issue I touched upon. What I should have said was, "in space, weight is money".
Every kg of non-payload you have to carry is something that could have been payload. Here are some ballpark figures [aviationweek.com] for orbiting
on a per-kilogram basis.

Don't get me wrong; it sounds like an interesting research project. Who knows, there
might be some point in the future where this technology offers the best

Nah, it's not that much. Not even close, since your spaceship weighs only a fraction of GLOW on reentry. Somewhere between a fifth and a tenth of GLOW. And dumping the wings is a considerable weight-saver, so it's not clear that those atmospheric effects are really buying you anything.

so it's not clear that those atmospheric effects are really buying you anything.

The atmospheric effects are buying you a safe trip to the ground. The atmospheric effects are what sheds all of that orbital speed. If you want to come down using a powered descent, then you're going to need to put as much energy into slowing the capsule as you put into getting it up to orbital speed in the first place. It is not a trivial amount of fuel, I would guess far more mass than a pair of wings and the cooling nit

You're thinking about this completely the wrong way. This is not actually cooling at all. They are injecting cold gas into the flow, against a positive pressure gradient. The pressure keeps the flow pressed against the surface of the craft, producing a protective film. The film prevents the craft from ever heating up in the first place. While this is a novel use of the technology, the technology itself is nothing new. It has been used for decades in rocket nozzles and gas turbines to protect the hot sections, and is a well understood and researched technique.

Of course, if real world science was as good as comics and speculative fiction have left us dreaming of , re-entry vehicles would be cooled by

Heat-Pump Lasers

or perhaps

Cryptoanalysis*

Seriously folks, scientifically speaking it takes *energy* to "do work", so for any given method of converting heat-energy into "work", if you give the problem enough *work* to do, it should pretty much initiate the next ice-age were said experiment to be conducted on a planetary surface.

In essence, the nitrogen pumped through the pores of the ceramic forms an "ablative" coating, as it absorbs and carries heat away from the surface of the craft. The nitrogen has to be refilled after every launch, but refilling a nitrogen tank is cheaper and easier than reapplying an ablative coating or repairing ceramic tiles.

Mixing liquid nitrogen and 10,000 degree re-entry friction temperatures... no thermal stress there! There is a reason why your father told you to never throw hot water onto your icy windshield to defrost it -- this sounds like the converse, throwing really cold liquid into a hot tile. Unless the tile has a thermal coefficient of expansion of zero, I'm betting this will crack some tiles.

I am glad we have you to make these observations, I am sure the scientist and engineers working on this project have not thought about such issues. I urge you to email them right away with your insight into their project.

I've just looked up the latent heat of vaporization of nitrogen and it's 200 kJ/kg [wikipedia]; its specific heat as a gas is around 1.1 kJ/kg/K, so to boil it and heat it to 1000K takes roughly 1.2 MJ/kg. The kinetic energy of an orbiting spacecraft is roughly 30 Mj/kg and even a spacecraft in a vertical trajectory that reaches 200 km has an energy of roughly 2 MJ/kg. So unless the spacecraft consists almost entirely of nitrogen tank, most of the heat of re-entry will have to go elsewhere. I propose that a better way to think about this cooling scheme is that the nitrogen is being ablated as a way to protect the ceramic tiles.

Does this mean it's a bad idea? Noooo! Replacing the ablated nitrogen is as simply as putting a hose in the tank after the craft lands, while inspecting and replacing ablated ceramic is one of the reasons why the Shuttle takes months to turn around (true fact: the most Shuttle missions NASA ever flew in one year was 10, in a year when they had four birds to fly, i.e. 48 bird-months, or 4.8 months per flight). Also, it seems likely that you can adjust the flow of nitrogen to get the temperature you want (within limits) instead of having to design tiles that can take whatever temperature Nature hands you. I wish these guys the best of German luck.

You're thinking about all wrong. Yes, the nitrogen is basically an ablative, but you missed a key aspect of reentry: radiative heat loss. Surfaces radiate heat proportional to their temperature to the fourth power. The hotter you can run them without them melting, the faster they radiate. The key point of a coolant isn't to keep the surface *cool*, but to keep it *cool enough* that it can radiate in peace without failing. You can't omit the radiative heat loss.

The nitrogen gas is not used as a heatsink, it is used to produce a protective film against the surface of the reentry craft. The film prevents the high temperature plasma from touching the craft, and is much more effective at keeping the craft cool then simply using it as a mechanism to dump the heat overboard.

I was under the impression that there was a fair amount of complex piping involved in the shuttles.

There is - but for cooling, hydraulics, etc... not heat shielding. And any Shuttle type replacement will require the same piping systems.So what I'm doing here is comparing like-to-like, the Shuttle's heat shielding system to this test vehicles heat shielding system.

How about the N2 is stored as liquid air doing double duty as O2 source and re-entry shield gas?

Being somewhat of a firearms geek, I've been reading up a lot on ballistics lately.

Rather than using airplane-like control surfaces & gliding wings that are basically dead weight until it comes time to use them as a huge airbrake & then as wings for an airplane-like landing after re-entry, what would be the feasibility of a vehicle shaped like a bullet with an extremely low coefficient of drag that would re-enter gradually through a series of ever-lower orbits through the upper atmosphere until it s

Aerobreaking and aerocapture have been used on several occasions as a mechanism for altering or entering orbit using a reduced amount of fuel. The version you are referring to is specifically called a 'skip renetry' and has been used on a handful of Russian orbital missions. http://en.wikipedia.org/wiki/Skip_reentry [wikipedia.org]

Isn't the hot air around the returning vehicle a plasma? If it is, can you repel it with proper use of electromagnetism?

Jon Goff, an aerospace engineer whose blog you should probably read in general because it's awesome and chock full of great aerospace analysis/ideas, had a rather intriguing discussion a few months ago about doing pretty much what you describe, applying magnetohydrodynamics to the problem of thermal protection during atmospheric reentry:

Something about re-entry has always troubled me and I'm hoping someone more familiar with the physics can answer it.

A spacecraft traveling at 18000MPH is in orbit then slams into the atmosphere, creating ram pressure that heats up the craft until it slows to a more acceptable atmospheric speed. The question is: why bother?

Couldn't a craft simply slow itself to a much more reasonable speed before re-entering the atmosphere with a thruster braking mechanism or some such? Is it just an issue of the fuel weigh

You are correct. If you had enough fuel you could brake the craft to a much lower speed.Think about all the fuel needed to tiny payload from the surface of the earth to orbit. You would need the same amount if you wanted to make a tail first landing back on the launch pad. Think of space ship one. It falls from space about 60 miles but with no tangential velocity. It makes it back with regular composites.

Not that this isn't a great tech demonstrator but why build a capsule that has a reusable heat shield? So you go through all of this trouble to build a beautiful reusable heat shield than slam it into an ocean or desert? Seems like you will be picking salt and sand out of it for a long time.
I've seen many Space Shuttle Landing in person and we are going to miss the ability to land a couple of miles away from the hangar.

Not that this isn't a great tech demonstrator but why build a capsule that has a reusable heat shield? So you go through all of this trouble to build a beautiful reusable heat shield than slam it into an ocean or desert?

There's a few possibilities. One is to use retrorockets, which are fired immediately before hitting the ground to give it a gentler landing. Another possibility that Boeing's seriously considering for their crew capsule is mid-air recovery (like that used on a number of unmannned return missions), where the capsule is caught by a helicopter as it's parachuting downwards, and can then be gently returned to a landing pad.

Another possibility that Boeing's seriously considering for their crew capsule is mid-air recovery (like that used on a number of unmannned return missions), where the capsule is caught by a helicopter as it's parachuting downwards, and can then be gently returned to a landing pad.

Imagine surviving launch atop a flaming stack of high explosives, the radiation of space and the hazards of re-entry to be dropped and splattered on the ground by a butter-fingered helicopter pilot.